High-frequency amplifier



May 8, 1951 J. E. YOUNG HIGH-FREQUENCY AMPLIFIER Original Filed Oct. 16, 1945 4 r v N Z 7 m Mug w M R u Y a 4 //M m% w y N R E O I}: l 'IIIHHII VF. T r FI I MN M Y B v a m 1:. I 0 M /J III IIL ll 5 J 6 6 25 FY Patented May 8, 1951 HIGH-FREQUENCY AMPLIFIER John E. Young, Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Original application October 16, 1945, Serial No. 622,603. Divided and this application January 21, 1947, Serial No. 723,425

3 Claims. (Cl. 179-171) This case, which is a division of my copending application Serial #622,603, filed October 16, 1945, now U. S. Patent 2,474,769 granted June 28, 1949, relates to high frequency apparatus and deals particularly with high power vacuum tube amplifying systems for short waves.

An object of my invention is to provide an improved high power amplifier system especially adapted for use at the higher frequencies. In carrying out this aspect of my invention, I make use of grounded grid power amplifier stages and circuits therefor which are especially free of, and the tendency to produce, parasitic oscillations. Also, I provide an improved cascaded arrangement of grounded grid amplifiers and circuits therefor which will develop substantial amounts of power at very short wave lengths.

A more detailed description of my present invention will now be given with the aid of the accompanying drawing wherein I have shown an improved power amplifier system, in accordance with my present invention, excited or driven by the frequency doubler, low power amplifier system of Figure 1 of my parent application. In the system illustrated herein, parasiticsa troublesome factor in high power operation-are minimized.

Referring to the drawing, wave energy is fed to the power amplifier I by way of a circuit involving a concentric transmission line II 4, I I8. As explained in my parent application, line II 4, I I8 is fed from a low power amplifier operating in the range of, for example, 78 to 108 megacycles. The output of this lower power amplifier may be a carrier lying in this band having a frequency modulation of :75 kilocycles. The outer conductor I I4 of the concentric line is grounded by connection H6 and the internal conductor H8 coupled by loop I to the cathode of power amplifier I00.

The output of amplifier I00 is fed to a succeeding power amplifier I22 similar in construction to amplifier I00. The output of the final power amplifier stage I22 is fed through a transmission line I24 and filter or harmonic attenuator I26 to a suitable broadcast antenna (not shown).

As shown, power amplifier I 60 is provided with a grounded grid type of vacuum tube. This tube is provided with a closed-01f cylindrical metal plate or anode I30 and grounded grid I32. The grounded gridsubstantially completely encloses and shields the bifilarly wound cathode I34 from anode I30.

The mid-point I36 of cathode I34 is connected by means of conductor or lead I38 and by-pass 2 condensers I39, I 4| to the cathode heating lead I42, I44 energized by the secondary of a cycle power transformer I46.

The lower end of metal tube or cylinder I40 surrounding the heating leads is grounded at I48. By means of a variable condenser I50 connected near its upper end, cylinder I40 is tuned so that the effective electrical length from the top of the cathode to ground is an odd multiple of a quarter wave length, here shown to be A of a wave length. In this way, the cathode vibrates at radio frequency potential with respect to ground, it being noted that the cathode, mid-point lead I38, metal tubular cylinder I40 and the heating conductors I42, I44 within it are effectively in parallel for radio frequency currents and voltages.

The grounding condenser I52 for the grid I32 is actually in the form of a metal ring or annulus, integral with the grid, brought through the glass seal of the vacuum tube, to the outside of the vacuum tube. This metal ring is capacitively ground at all points on its circumference by means of a similar metal ring separated by an annular insulator located between both metal rings. The annular capacitor is indicated diagrammatically at I 52 and this capacity is shunted by a suitable leak resistor I54. By-pass condensers I5I and I53 tie the heating leads to ground for radio frequency currents.

The metal anode I30 has mechanically and electrically fixed thereto radial metal cooling fins I3I. Surrounding and connected to the fins is a metal cylinder I54 shown in cross section. This metal cylinder I54 forms the inner conductor of a concentric line tank circuit, the outer surrounding conductor of which is in the form of a grounded metallic cylinder I56, also shown in cross section. The upper outer end of inner conductor I54 is capacitively coupled to the inner surface of outer conductor I56 at point I58 so that the effective electrical length of the anode circuit is an odd multiple of a quarter wave length, here shown as one-cuarter of a wave length. between the anode and the capacitive grounding po nt I58,

The adjustable capacitive grounding system I 58 consists of a pair of annular rings of insulating material I60, I62. These rings may be made of a material known as micalex. The upper and lower faces of the rings are coated with a metal such as silver or copper. The upper faces or electrodes I10, I12 are electrically connected toe gether by bolts I14. The latter may also serve to hold the rings I60, I62 together, but insulatingly separated by insulating cylinders or washers surrounding connectors I'I4. By means of spring fingers I80 in electrical contact with the upper faces I72, sliding electrical contact is made with the inner surface of outer conductor I56.

Similarly, by means of connectors I82, the lower metallic faces of the disc or rings I60, I66 are connected in parallel and by means of metal connecting fingers I84 sliding electrical contact is made to the outer surface of inner conductor I54. It will be observed, therefore, that the capacities formed by the annular insulating rings I60, I62 and their metal faces H0, I12 and I86, I88 are in parallel, thereby increasing the effective capacity at the point I58. In this way the outer and inner conductors are connected together at point I58 by a connection of low impedance to radio frequency currents while separated electrically for direct current voltages.

Adjustment of the capacitive system I58 is effected by means of the rack I90 mechanically fastened to the capacitor assembly I58 and cooperating gear I92 which may be provided with an externally operable, rotatable drive shaft I94. Rotation of gear I92 drives rack I90 up or down, thereby moving capacitor assembly I58 along the longitudinal axis of the concentric line system I54, I56 thereby varying, as desired, the effective electrical length of the tank circuit I54, I56.

Plate voltage for power amplifier I is fed from a rectifier 200 and lead 202 to the inner conductor I54 of the plate tank circuit.

By means of coupling loop 206, preferably made variable, and a concentric transmission line 203, output energy is taken from amplifier I00 and fed to the following amplifier I22 by way of the loop 2I0 and cathode system 2I2 of power amplifier I22. Coupling loop 2I0 and cathode system 2I2 correspond in structure to loop I and cathode system I40 of amplifier I00. Also, since amplifier I22 is identical in all essential respects with amplifier I00, it has been shown only schematically and will not be described in detail.

Output from amplifier I22 is taken from an inductive loop 2H5 corresponding in structure to loop 206 and fed through transmission line I24 and harmonic attenuator or band pass filter I26 to an antenna.

Cooling air may be blown by a suitable blower (not shown) through the inner conductor I54 and through fins I3 I, escaping in part by way of openings 300 in the outer conductor I56.

In practice, I prefer to set up the apparatus of the drawing so that it is inverted with respect to the position illustrated. That is, the apparatus is supported and mounted so that the vacuum tubes, such as I30, and the leads thereto are uppermost. Also, in this preferred arrangement air is forced up from the bottom through the inner tubular conductors, such as I54, and the choke coil in power supply lead 202 is supported in the air stream at a point below the concentric line structures.

Having thus described my invention, what I claim is:

1. A high frequency amplifier comprising a vacuum tube having a directly heated cathode whose two sides are joined at one end removed from the source of heating supply, said tube having an anode surrounding said cathode and provided with cooling fins and a grid intermediate said cathode and anode, a pair of leads connecting said cathode to a source of heating supply,

a metallic cylinder surrounding said leads, a connection capable of passing direct current from a point on said cylinder removed from said cathode to ground, an adjustable tuning capacitor cou- "pling another point on said cylinder nearer said cathode to ground, bypass capacitors across said pair of leads at a point adjacent said cathodes, bypass capacitors from said leads to said cylinder near said ground point, a bypass capacitor coupling said grid to ground, an adjustable concentric line tank circuit coupled to said anode, said tank circuit having a hollow inner conductor coupled at one end to said anode and a surrounding outer conductor extending past said anode, means for supplying waves to be amplified to said cylinder, and means for deriving the amplified output from said tank circuit.

2. A high frequency amplifier comprising a vacuum tube havin a bifilarly wound cathode provided with a midpoint, an anode surrounding said cathode, and a grid intermediate said cathode and anode, a concentric line tank circuit having a hollow inner conductor connected to said anode and an outer conductor extending past said anode, a tuning capacitor across said tank circuit at a location approximately onequarter of a wavelength away from the open end of said outer conductor at the operating frequency, a bypass capacitor connecting said grid to ground, a pair of leads connecting said cathode to a source of heating supply, a metallic cylinder surrounding said heating leads, bypass capacitors between said leads and said midpoint of said cathode at a location near said cathode, an adjustable tuning capacitor coupling said cylinder to ground at a location near said cathode, a direct connection to ground from said cylinder at a location removed from said adjustable capacitor, bypass capacitors between said leads and said cylinder near said last location, said adjustable capacitor havin such value that the efiective electrical length from the end of said cathode farthest away from said heating leads to ground is an odd multiple of a quarter wavelength at the operating frequency, and means for feeding said amplifier with waves to be amplified at a location on said cylinder intermediate the adjustable tuning capacitor and said ground connection.

3. A high frequency amplifier as defined in claim 2, characterized in this that said vacuum tube is a forced air-cooled triode provided with cooling means forcing air through one end of the hollow inner conductor of said concentric line tank circuit at the location farthest removed irom said anode.

JOHN E. YOUNG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,157,855 Koch May 9, 1939 2,235,414 White Mar. 18, 1941 2,342,897 Goldstine Feb. 29, 1944 2,419,793 Rosencrans Apr. 29, 1947 2,419,800 Tomlin Apr. 29, 1947 2,463,724 Starner Mar. 8, 1949 FOREIGN PATENTS Number Country Date 556,054 Great Britain Sept. 17, 1943 

